Alpha Technologies Lomain Ni-Cd Pocket Plate Battery - Manual (Page 11)

11 745-680-B10-001 Rev. A
1.0 Introduction, continued
1.1 Theory of Operation
A standard Ni-Cd flooded battery type needs to be topped up with distilled water after a
certain period of time depending on charging regime and operating temperature. The loss of
water during overcharge is caused by the following chemical reaction:
At the positive plate 4OH-→ 2H2O + O2 + 4e -Oxygen Evolution
At the negative plate 4H2O + 4e -→ 2H2 + 4OH-Hydrogen Evolution
In theory, the quantity of water used according to Faraday’s equation is that each ampere
hour of overcharge breaks down 0.336 cm 3 of water. While charging a Ni-Cd battery oxygen
evolution occurs just before the positive plate reaches its fully state of charge and reaches
its peak if it becomes fully charged. Since the negative plate provides a much better charge
acceptance than the positive plate hydrogen is not evolved until it has reached its
fully-charged state.
In order to reduce the water consumption Alpha Lomain-concept has been developed based
on four distinctive key features:
Plate design
Seperation system
Venting system
Cell design
Special plate design
Alpha Lomain batteries have been designed with an excess of negative material (cadmium)
to ensure that oxygen evolution occurs prior to hydrogen evolution to enhance the above
mentioned effect.
Oversized negative plate
Felt seperator
Fig. 2, Detail of plate design